Injection devices for injection of medicaments into a patient are generally known. Such devices include, for example, traditional hypodermic needle syringes that contain a stock of medicament therein. Upon insertion of the needle under the patient's skin at an injection location, the medicament is forced out of the syringe and through the needle by depression of a plunger mechanism.
Injection devices also include needle-free injectors, some of which are described in U.S. Pat. Nos. 5,599,302; 5,062,830; and 4,790,824; and needle-assisted injectors, such as those described in U.S. Patent Publication No. 2005/0033234. These jet injectors administer medicaments as a fine, high velocity jet delivered under sufficient pressure to enable the jet to pass through the skin, or for improved dispersion of the injected medicament. Self-injectors or autoinjectors like the ones disclosed in U.S. Pat. Nos. 4,553,962 and 4,378,015, and PCT Publications WO 95/29720 and WO 97/14455 are constructed to inject medicament at a rate and in a manner similar to hand-operated hypodermic syringes.
These injectors often are made for a single use, or alternatively to be refilled after each injection. Some refillable injectors can be refilled with a desired dosage to be injected. Upon injection, the entire loaded dosage is injected.
An injector is needed that can deliver a medicament into a patient in an adjustable dose that is equal to or less than the full amount contained in the injector.